Recently techniques have become available for the non-invasive stimulation of the human cortex and deep proximal peripheral nerves. Stimulation can be with a high voltage, extremely brief electrical pulse or with magnetic stimulation. One purpose is to use these methods for noninvasive localization of different parts of the human cortex including motor cortex, sensory cortex and language cortex. Another purpose is to study cortical physiology in different disease states. We have made a number of advances in understanding the technical aspects of magnetic stimulation, trying to define the optimal method to map different body part representations in motor cortex. In detailed mapping studies, distal muscles were significantly more excitable than proximal muscles and motor representations targeting proximal arm muscles were significantly more excitable in the right than in the left hemisphere. Plastic reorganization of the brain has been demonstrated in a number of circumstances. In amputees, muscles ipsilateral to the stump could be activated from a larger area than those contralateral to the stump. In patients with spinal cord injury, magnetic stimulation evoked larger motor evoked potentials with shorter latencies in muscles immediately proximal to the level of a spinal cord injury than in corresponding muscles in controls. In patients with hemispherectomy, stimulation of the remaining hemisphere evoked bilateral muscle responses in proximal and distal muscles at similar latencies indicating a bilateral representation of arm muscles and the existence of physiologically active ipsilateral pathways. Detailed mapping studies have also been done with paresthesias produced by magnetic stimulation. Akinesia in Parkinson's disease was studied with motor evoked potentials elicited prior to a reaction time movement. Results showed that it took longer than normal for patients to bring the cortex to a sufficient level of excitation to produce a voluntary movement.